New study finds intact rainforests of Borneo are getting larger

The remaining undisturbed rainforests in Borneo, some of the world’s tallest and most carbon-dense, have been removing carbon dioxide from the atmosphere over the past 50 years, a new study shows.

The research, led by the
University of Leeds, found that while the intact forest area has declined, those that remain have increased in biomass. The study quantifies for the first time the role of South East Asian
tropical rainforests in the fight against climate change.

An international team of
more than 50 scientists monitored tens of thousands of trees in over a dozen
locations across Borneo for up to half a century, revealing the rainforests
steady increase in biological material - biomass - as well as its vulnerability
to climate and land-use changes.

Lead author Dr Lan Qie,
who carried out the work whilst at the University of Leeds School
of Geography, said:
Borneos remaining rainforests are increasing in size, adding to their already
high carbon stocks.

The average increase we
saw in Borneo is equivalent to adding 700 household Christmas trees to each 100
metre by 100 metre forest plot, each year. There is of course both growth and
death in these towering and dynamic tropical forests, but on the whole they are
absorbing more carbon year after year, storing it as wood.

The teams research,
published today in Nature Communications,
shows that Borneos average increase in forest biomass carbon, 430kg per hectare per year, is
consistent with the increases shown across the tropical African and Amazon
forests in the past.

Measuring the trees in the Borneo rainforest. Picture by Dr Lan Qie

Co-author Professor Simon
Lewis, also from the University of Leeds, said: After conducting dozens of
field campaigns across the tropics over the past two decades, we can now
finally say that the worlds remaining intact tropical forests, across the Amazon,
Africa and Asia, are all acting as carbon sinks  absorbing more carbon than
they are releasing.

It is now clear that undisturbed
tropical rainforests across the world are all providing an important service to
humanity in removing carbon from the atmosphere, adding a further reason to
protect these vulnerable forests.

The international forest
monitoring network of researchers that contributed to this work was developed
with support from a European Research Council grant awarded to Professor Oliver
Phillips and Professor Simon Lewis, both at the University of Leeds.

Forests under threat

The study highlights two
threats to continued carbon uptake by rainforests: droughts and forest
fragmentation.

Co-author Professor Oliver
Phillips, from the University of Leeds, said: By monitoring forests before,
during and after the 1997-1998 El Niño drought we were able to show how the
drought killed trees, so returning carbon to the atmosphere and halting the
forests ability to act as a carbon sink.

This illustrates the risk
posed by future droughts, which climate models suggest will become more severe,
as rainforests across the globe may temporarily pause in their roles as carbon
sinks.

The study also highlights
concerns about the carbon uptake in fragmented patches of forests  sections of
forest that are isolated from the larger forest. Monitored forest areas close
to the edge of a patch, which may be adjacent to burnt land, oil palm
plantations or farmers fields, tended to lose carbon to the atmosphere. Trees
were more likely to die if they were closer to the edge, and the tree species
that replace them tended to be those that store less carbon.

Treetops of Borneo's rainforest. Picture by Dr Lan Qie

Dr Lan Qie, who is now at
Imperial College London, added: Our
calculations indicate a minimum size that a patch of forest must be in order
for it to be a carbon sink - where its interior is absorbing enough carbon to
outweigh its edges, which may be losing carbon. A forest reserve of 300
hectares, a little over one square mile, is just about big enough.

We must aim to preserve
larger areas of continuous forest, and protect against further fragmentation,
in order to maintain its ability to uptake carbon emitted by human activity.

Effective buffer zone management
can also reduce carbon loss along forest edges and very small forest fragments
can still help protect carbon. Preserving existing fragments of forest of any
size remains important, for both carbon storage and biodiversity conservation.

Professor Simon Lewis,
from the University of Leeds, added: This study can provide a foundation for
future long-term observations of Asias tropical forests, delivering essential
baseline information on how these globally important ecosystems are responding
to rapid global environmental change.

The research paper Long-term carbon sink in Borneos forests halted by drought and vulnerable to edge effects is published 19 December 2017 in the journal Nature Communications and is available online.

Further information

Images courtesy of Dr Lan Qie

For additional information
and to request interviews please contact Simon Moore in the University of Leeds
press office on +44 (0)113 34 34031 or s.i.moore@leeds.ac.uk.

This research was
conducted by a global team of over 50 scientists, drawing on work dating back
to the 1960s. This work was supported by a European Research Council grant
awarded to Professor Oliver Phillips and Professor Simon Lewis, both at the
University of Leeds.

Christmas
trees calculations:

Borneos average increase
in forest biomass carbon is 430kg per hectare (100 metre by 100 metre) per
year. A ~2.6m tall Norway spruce (Picea abies) with a diameter of 2-3 cm
at breast height is used for a reference Christmas tree. Typically a Norway
spruce of this size contains ~1.2kg dry biomass (which contains about 0.6 kg
carbon) therefore 430kg carbon per hectare is approximately 700 Christmas trees
added to each forest plot.